Young men who have sex with men (YMSM) have an alarming HIV/AIDS prevalence and are also one of the only risk groups showing an increasing rate of infections. Network research is a current priority area due to HIV's high transmission dependence on sexual and drug network dynamics; however, few studies have examined the networks of YMSM. In order to advance knowledge of the drug and sexual networks of YMSM and how these networks influence HIV transmission, this study proposes to construct and analyze a macro- network of YMSM by utilizing data already being collected within two NIDA-funded parent studies. These two studies have gathered a sample of 175 YMSM and are investigating their drug, sex, and social networks, and are also collecting data on the prevalence, developmental trajectories, and predictors of HIV and multiple psychosocial health issues linked to the disease (syndemic outcomes). Although these studies are an important first step, the network data collected is ego-centric (or personal network) in nature. While ego-centric data can contribute to understanding the relationships individuals have within their personal networks and possible influence on HIV, many network measures cannot be accurately assessed with ego-centric data (i.e., distance, centrality, positional equivalence). Additionally, ego-centric data may be biased as particular network members (alters) may appear many times across ego-centric networks. And finally, disease spread between networks cannot be measured. This study is a two-phase project that proposes to link the previously collected ego-centric networks of these YMSM by matching the already collected identifying information of alters and building a macro-network of YMSM. A network such as this has never been collected with YMSM, and will lead to new and important analyses. We will create these links using probabilistic matching software. Phase 1 of the project will focus on the construction of the macro-network of YMSM. Phase 2 of the project will analyze the macro-network with the following sub-aims: A) Examine the macro-network structure of YMSM and determine how these network structures differ by individual characteristics; B) Analyze HIV transmission and behavior contagion (e.g. the spread of condom and drug use); C) Identify the key individuals within the macro-network (bridge drug- and sex-network individuals) and those who may hold the most influence (high centrality social- network individuals); D) To describe overlap in drug use and HIV risk behaviors within the macro-network; and, finally E) To examine the value of macro-network structures in the prediction of syndemic outcomes.